This invention relates to hydraulic actuators and more particularly to retainer assemblies for use with hydraulic actuators.
Hydraulic actuator apparatus are known for operating a mechanism at a remote location by way of a master cylinder connected to a slave cylinder installed at the remote location. A conduit interconnects the master cylinder and slave cylinder, and the hydraulic apparatus is filled with hydraulic fluid such that, when the piston of the master cylinder is actuated, the piston of the slave cylinder, and consequently the piston rod or output member of the slave cylinder, is simultaneously actuated by displacement of the hydraulic fluid from the master cylinder to the slave cylinder through the conduit.
More particularly, it is known to provide such hydraulic apparatus for operating the release mechanism of a friction clutch. As disclosed in U.S. Pat. No. 4,599,860 assigned to Automotive Products plc. of Warwickshire, England, it is also known to preassemble friction clutch hydraulic release apparatus by filling the master cylinder, the slave cylinder and the interconnecting conduit with hydraulic fluid prior to shipment of the assembly to a motor vehicle manufacturer for installation on the motor vehicle.
Prior to installation on the motor vehicle, the piston rod or output member of the slave cylinder may become extended. Such pre-installation extension is undesirable since the extended slave cylinder now occupies more space than necessary in the shipping container, since the extended rod may become bent or damaged or become disconnected from the piston during transit or storage, since the pressure of the fluid in the apparatus may drop below atmospheric with the result that air may be introduced into the apparatus, and since the slave cylinder must be manually retracted and held retracted during installation of the apparatus in the motor vehicle.
In order to avoid all of these problems related to inadvertent extension of the output member of the slave cylinder prior to installation in the motor vehicle, it has been proposed to provide a rupturable shipping strap for the slave cylinder which maintains the output mmber of the slave cylinder in a retracted position until the slave cylinder is installed in the motor vehicle, whereafter the master cylinder is actuated to pressurize the system and extend the output member of the slave cylinder to rupture the shipping strap. A shipping strap of this general type is disclosed in U.S. Pat. No. 4,454,632, also assigned to Automotive Products plc. In order to avoid inadvertent rupture of the shipping strap prior to installation in the vehicle as a result of inadvertent actuation of the master cylinder, it has been proposed to provide a restraining clip for installation on the piston rod of the master cylinder to prevent accidental operation during shipping and installation. Such a clip, which is removed at such time as the installation of the slave cylinder in the vehicle has been completed to allow the system to be thereafter actuated to rupture the shipping strap, is shown in U.S. Pat. No. 4,581,979, also assigned to Automotive Products plc.
There are some situations, however, in which the use of such a restraining clip on the master cylinder piston rod is not feasible. For example, when a control switch assembly is positioned on the master cylinder piston rod to selectively control various systems of the vehicle in response to actuation of the master cylinder piston rod, it is no longer possible to employ a restraining clip on the master cylinder piston rod and it becomes necessary to provide other means to prevent inadvertent operation of the master cylinder, with resultant rupture of the shipping strap, prior to installation of the slave cylinder in the motor vehicle.